Zeolites are crystalline aluminosilicate compositions which are microporous and which are formed from corner sharing [AlO4/2]− and SiO4/2 tetrahedra. Numerous zeolites, both naturally occurring and synthetically prepared are used in various industrial processes. Synthetic zeolites are prepared via hydrothermal synthesis employing suitable sources of Si, Al and structure directing agents (SDAs) such as alkali metals, alkaline earth metals, amines, or organoammonium cations. The structure directing agents reside in the pores of the zeolite and are largely responsible for the particular structure that is ultimately formed. These species balance the framework charge associated with aluminum and can also serve as space fillers. Zeolites are characterized by having pore openings of uniform dimensions, having a significant ion exchange capacity, and being capable of reversibly desorbing an adsorbed phase which is dispersed throughout the internal voids of the crystal without significantly displacing any atoms which make up the permanent zeolite crystal structure. Zeolites can be used as catalysts for hydrocarbon conversion reactions, which can take place on outside surfaces of the zeolite as well as on internal surfaces within the pores of the zeolite.
In 1982, Wilson et al. developed aluminophosphate molecular sieves, the so-called AlPOs, which are microporous materials that have many of the same properties of zeolites, but are silica free, composed of [AlO4/2]− and [PO4/2]+ tetrahedra (See U.S. Pat. No. 4,319,440). Subsequently, charge was introduced to the neutral aluminophosphate frameworks via the substitution of SiO4/2 tetrahedra for [PO4/2]+ tetrahedra to produce the SAPO molecular sieves (See U.S. Pat. No. 4,440,871). Another way to introduce framework charge to neutral aluminophosphates is to substitute [M2+O4/2]2− tetrahedra for [AlO4/2]− tetrahedra, which yield the MeAPO molecular sieves (see U.S. Pat. No. 4,567,029). These MeAPO materials generally showed low substitution levels of M2+ for Al3+, generally on the order of 10%, while several materials, notably MeAPO-44 exhibited M2+ for Al3+ substitution levels of 40%. Later, MeAPO-50 also showed nearly 40% substitution of M2+ for Al3+, but these examples of high Me2+ substitution were few (See ZEOLITES, 1995, 15, 583-590). It is furthermore possible to introduce framework charge on AlPO-based molecular sieves via the introduction both of SiO4/2 and [M2+O4/2]2− tetrahedra to the framework, giving MeAPSO molecular sieves (See U.S. Pat. No. 4,973,785).
Before the SAPO materials of U.S. Pat. No. 4,440,871 were known, there were attempts to make “phosphate zeolites,” i.e., substitution of phosphorus for silicon in an aluminosilicate. Such a substitution in an aluminosilicate zeolite, [PO4/2]+ for [SiO4/2], represents a reduction of the negative charge on an aluminosilicate framework. The initial work by Flanigen and Grose co-precipitated the components of silicoaluminophosphate gels, isolated the resulting solid, suspended the resulting solids in alkali hydroxide solutions and treated them under hydrothermal conditions, yielding a series of phosphate zeolites, including those of LTL, CHA, LTA, and GIS topologies (See E. M. Flanigen and R. W. Grose, ADVANCES IN CHEMISTRY Series No. 101, ACS, Washington D. C., 1971). The low phosphate preparations, P/Al≤1.1, resulted in alkali silicoaluminophosphate species that were not as thermally stable as their aluminosilicate analogs, often less than 350° to 400° C., and reduced adsorption capacity in some cases suggest the possibility of some occluded phosphate in pores and cages. Similarly, Wacks et al. disclose a process for preparing silicoaluminophosphate zeolites that entails digesting hydrated aluminophosphate solids in the presence of sodium silicate solutions to make the desired silicoaluminophosphate materials, in which the claimed range of phosphate incorporation was given by P2O5/Al2O3=0-0.2, suggesting that Al/P≥5 in these materials (See K. Wacks et al., U.S. Pat. No. 3,443,892). While eight examples of this zeolite synthesis process are disclosed in U.S. Pat. No. 3,443,892, there is no data offered that shows that any P was actually incorporated into the zeolite product; a possibility given the claimed range extends to zero. Many attempts to make silicoaluminophosphate zeolites resembled reactions that would be used to make aluminosilicate zeolites, but carried out in the presence of phosphate, yielding little phosphate incorporation. Kuhl conducted syntheses of silicoaluminophosphate compositions, employing high levels of both phosphate and hydroxide, utilizing a combination of tetramethylammonium and sodium hydroxides for the latter, to make the LTA-related species ZK-21 and ZK-22 (See G. H. Kuhl, INORGANIC CHEMISTRY, 10, 1971, p. 2488). These species exhibit low phosphate incorporation, Al/P>8.9, and it was concluded that the phosphate was occluded in zeolitic cages rather than incorporated into the framework. Casci et al. disclose low phosphate chabazite materials in which the framework phosphorus is claimed to be between 0.05-5 mole %, i.e., P/(Al+Si+P)=0.0005−0.05 (See US 2014/0193327). The amount of phosphate employed in the reaction mixtures of the examples is low (Al/P>5.5) and no data is offered in the examples to show what the P incorporation actually is. An outlier disclosed in the SAPO patent (U.S. Pat. No. 4,440,871) uses some sodium aluminate, tetramethylammonium hydroxide and low phosphate (P/Al=0.4) to prepare SAPO-42 (Example 48), which has the LTA topology and a composition similar to that of ZK-21 and ZK-22 mentioned above as Al/P>10. The SAPO-42 product is described in the application by an essential formulation that does not include alkali, since U.S. Pat. No. 4,440,871 only covers compositions of the formulation mR:(SixAlyPz)O2. This patent application also discloses the synthesis of SAPO-20 from the same reaction mixture treated at higher temperature (Example 28). The SAPO-20 product, which has the SOD topology, is not porous, but has a slightly enhanced P content as Al/P=3.17. For many years now, a large gap has been present in the known compositions of microporous silicoaluminophosphates, between the SAPOs disclosed in U.S. Pat. No. 4,440,871 and what are essentially the “phosphate zeolites” reviewed above. In particular, the materials of intermediate silicon and phosphorus levels are missing. These are materials of intermediate charge density, of higher charge density than the SAPOs originating from low level substitution of Si into neutral AlPO frameworks, but lower charge density than the phosphate zeolites.
A similar charge density gap exists for MeAPO-based materials. In the early 1990's, high charge density Me2+-P—O based molecular sieves, similar to the MeAPOs of U.S. Pat. No. 4,567,029 but without the Al, were developed by Bedard (See U.S. Pat. No. 5,126,120) and Gier (See U.S. Pat. No. 5,152,972). These metal phosphates (sometimes arsenates, vanadates) were based on M2+ (M=Zn, Co), the general formula of which, in terms of the T-atoms, T2+-T5+, was approximately A+T2+T5+O4, having framework charge densities similar to Si/Al=1 zeolites and were charge balanced by alkali cations, A+, in the pores. Later attempts to prepare metallophosphates of similar compositions but with organic SDAs led to porous, but interrupted structures, i.e., the structures contained terminal P—O—H and Zn—N bonds (See J. MATER. CHEM., 1992, 2(11), 1127-1134). Attempts at Al substitution in a zincophosphate network was carried out in the presence of both alkali and quaternary ammonium agents, specifically the most highly charged quaternary ammonium species, tetramethylammonium, but because of the high framework charge density, only the alkali made it into the pores to balance framework charge (See U.S. Pat. No. 5,302,362). Similarly, in a high charge density zincophosphate system that yielded the zinc phosphate analog of zeolite X, the synthesis in the presence of Na+ and TMA+ yielded a product that contained considerably less TMA+ than Na+ (See CHEM. MATER., 1991, 3, 27-29).
To bridge the rather large charge density gap between the MeAPOs of U.S. Pat. No. 4,567,029 and the aforementioned alkali-stabilized Me2+-phosphates of Bedard and Gier, Stucky's group developed a synthesis route using amines, often diamines in ethylene glycol. They were able to make high charge density, small pore MeAPOs in which the concentrations of Co2+ and Al3+ in R(CoxAl1-x)PO4 were varied such that 0.33≤x≤0.9 in the so-called ACP series of materials, the aluminum cobalt phosphates (See NATURE, 1997, 388, 735). Continuing with this synthesis methodology utilizing ethylene glycol reaction mixtures and matching the amines to framework charge densities for R(M2+xAl1-x)PO4 such that 0.4≤x≤0.5, (M2+=Mg2+, Mn2+, Zn2+, Co2+), the large pore materials UCSB-6, -8 and -10 were isolated (See Science, 1997, 278, 2080). Similarly, this approach also yielded MeAPO analogs of zeolite rho of the composition where RM2+0.5Al0.5PO4, where R═N, N′-diisopropyl-1, 3-propanediamine N2+═Mg2+Co2+ and Mn2+. Cowley followed this ethylene glycol-based approach, which he described as “predominantly non-aqueous solvothermal conditions” to synthesize a high charge density CoGaPO-5, (DABCO)2[Co4Ga5P9O36], with the DABCO SDA (See ZEOLITES, 1997, 18, 176-181). Cowley also utilized this strategy to prepare cobalt and zinc gallium phosphates using quinuclidine as the SDA, one of which has the CGS topology with a framework charge density of −0.125/T-atom (See MICROPOROUS AND MESOPOROUS MATERIALS 1999, 28, 163-172). Similarly, Lin and Wang used 1,2 diaminocyclohexane (DACH) with the ethylene glycol approach to prepare a Zn—Ga phosphate of CGS topology with higher Zn incorporation than the Cowley work, realizing a framework charge density of −0.25/T-atom for (H2DACH)Zn2Ga2(PO4)4 (See CHEMISTRY OF MATERIALS, 2000, 12, 3617-3623). The reliance of this non-aqueous synthesis approach on ethylene glycol solvent does not lend itself well to industrial scale, from both a safety and environmental point of view. This non-aqueous approach also leads to very large crystals, often with dimensions of hundreds of microns, which are too large for industrial use, where μ-sized or smaller crystals are often preferred (See SCIENCE, 1997, 278, 2080). Other than this work cited here, there has been little activity in this intermediate charge density region, where 0.2≤x≤0.9 for the [M2+xAl1-xPO4]x− compositions.
Pursuing aqueous chemistry, Wright used highly charged triquaternary ammonium SDAs to make new MeAPO materials (See CHEM. MATER., 1999, 11, 2456-2462). One of these materials, STA-5 with the BPH topology, (Mg2.1Al11.9P14O28), exhibited significant substitution of Mg2+ for Al3+, up to about 15%, but less substitution than seen in Stucky's non-aqueous ethylene glycol approach.
Unlike the SAPO and MeAPO chemistry discussed in the previous paragraphs, there has been far less investigation in the MeAPSO compositional arena, perhaps because of the complicated nature of this 4-component class of materials. The MeAPO and SAPO materials already consist of 3 T-atom components derived from substitution of Me2+ or Si into AlPO-based frameworks, respectively. In the prior art, the addition of the fourth T-atom component, either Si or Me2+, has generally been a perturbation of an existing MeAPO or SAPO material. Flanigen et al. review aluminophosphate molecular sieves and the periodic table and discuss the elements that may be substituted into AlPO-based frameworks along with the elements that have been incorporated in 22 different AlPO-based topologies (See Y. Murakami, A. Lijima, J. W. Ward (Eds.), Proc. of 7th Int. Zeolite Conf, (Elsevier Amsterdam 1986), p. 103-112). In each case where a MeAPSO composition exists, there is also an AlPO, SAPO, or MeAPO composition except for MeAPSO-46, which was actually found first as a MeAPSO composition, but later found in a MeAPO composition with the same SDA, di-isopropylamine (See J. CHEM. SOC., Faraday Trans., 1993, 89, 4141-4147). There are many examples of MeAPSO compositions that are derivatives of previously known MeAPO or SAPO compositions, for instance MeAPSO-34, the derivatives often prepared to see the effects on catalytic and other material properties (See APPLIED CATALYSIS A, General 2011 406, 59-62). The MeAPSO compositions, however, have not been the focus of new exploratory synthesis. For instance, the attempts to make higher charge density metalloaluminophosphates by Stucky, Cowley and others discussed above have not been extended to MeAPSO compositions. Hence, more than the MeAPOs and SAPOs discussed above, there is a lack of MeAPSO compositions of intermediate to high charge density, in other words, MeAPSOs that contain significant amounts of Me2+, Si4+, or both, above the minor to modest substitution levels described in U.S. Pat. No. 4,973,785. In short, the compositions of MeAPSO materials have not progressed from what was disclosed in U.S. Pat. No. 4,973,785.
More recently, Lewis et al. developed aqueous solution chemistry leading to higher charge density SAPO, MeAPO, and MeAPSO materials, enabling greater substitution of SiO4/2 and [M2+O4/2]2− into the framework for [PO4/2]+ and [AlO4/2]−, respectively, using the ethyltrimethylammonium (ETMA+) and diethyldimethylammonium (DEDMA+) SDAs. These materials include MeAPO, SAPO, and MeAPSO versions of ZnAPO-57 (U.S. Pat. No. 8,871,178), ZnAPO-59 (U.S. Pat. No. 8,871,177) and ZnAPO-67 (U.S. Pat. No. 8,697,927), as well as the species MeAPSO-64 of BPH topology (U.S. Pat. No. 8,696,886), which was not realized as a MeAPO or SAPO composition with these SDAs. The relationship between the increasing product framework charge densities and reaction parameters, namely the ETMAOH(DEDMAOH)/H3PO4 ratios, were outlined in the literature (See MICROPOROUS AND MESOPOROUS MATERIALS, 189, 2014, 49-63).
Applicants have now synthesized a new family of high charge density metalloalumino(gallo)phosphosilicate framework molecular sieves. These materials exhibit higher charge densities than the MeAPSOs mentioned in U.S. Pat. No. 4,973,785, most notably containing either more Me2+, more Si4+ or both. The high charge density (HCD) MeAPSOs of this invention are synthesized in a mixed quaternary ammonium/alkali SDA system, for example ETMA+/K+. The utilization of alkali in AlPO-based systems is uncommon and is required here to achieve the higher charge density and higher Me2+ and Si4+ incorporation. The MeAPSO materials of this invention are crystalline microporous compositions and often contain “Si islands,” regions of “Si—O—Si” bonding.